Golang golang-prime (snippet)

Go programming example 'golang-prime'

golang-prime

Golang beginners example: golang-prime

package main

import (
    "flag"
    "fmt"
    "os"
    "strconv"
)

func Sqrt(n int) int {
    var t uint
    var b uint
    var r uint
    t = uint(n)
    p := uint(1 << 30)
    for p > t {
        p >>= 2
    }
    for ; p != 0; p >>= 2 {
        b = r | p
        r >>= 1
        if t >= b {
            t -= b
            r |= p
        }
    }
    return int(r)
}

func getPrime(n int) int {
    var primeList = []int{2}
    var isPrime int = 1
    var num int = 3
    var sqrtNum int = 0
    for len(primeList) < n {
        sqrtNum = Sqrt(num)
        for i := 0; i < len(primeList); i++ {
            if num%primeList[i] == 0 {
                isPrime = 0
            }
            if primeList[i] > sqrtNum {
                i = len(primeList)
            }
        }
        if isPrime == 1 {
            primeList = append(primeList, num)
        } else {
            isPrime = 1
        }
        num = num + 2
    }
    return primeList[n-1]
}

func main() {
    flag.Parse()
    s := flag.Arg(0)
    i, err := strconv.Atoi(s)
    if err != nil {
        fmt.Println("please provide a number")
        os.Exit(2)
    }
    fmt.Println(getPrime(i))
}

Useful links

• Learn Go: https://golangr.com
• Download Go: https://golang.org